Amiga 500 Capacitor Replacement Guide

Commodore's layout drawing for the Rev. 5 main board, PCB assembly 312510

The tables below list the electrolytic capacitors on the Amiga 500 main boards and on the A501 RAM and clock expansion, as printed in Commodore's Service Manual A500 (PN-314981-04, October 1990). Ceramic and film capacitors are not listed here; the same pages give their values.

The A500 uses through-hole electrolytics, and repairers report far fewer capacitor failures on it than on the surface-mount Amiga 600 and Amiga 1200. Not everyone agrees that a working A500 can be left alone: one AmiBay contributor expects 25-year-old A500 capacitors "to eventually start to cause random crashes, boot failure". The external power supply and the A501's battery have failures of their own; see the Amiga 500 Maintenance Guide.

Identify the board

Commodore's manual covers two main boards. Rev. 5 is PCB assembly 312510 with schematic 312511-02; Rev. 6A/7 is assembly 312510-07 (NTSC) or 312510-08 (PAL) with schematic 312511-03. The easiest difference to see is the chip RAM: sixteen 256K × 1 DRAMs at U16-U31 on Rev. 5, four 256K × 4 DRAMs at U16-U19 on Rev. 6A/7. The early Rev. 3 board also has sixteen RAM chips, and the manual has no list for it. Dave Farquhar separates the two by the marking above the RAM: a Rev. 5 board has a white silkscreened "A500" there, while on a Rev. 3 board the identifier is etched into the copper. From the trapdoor, a Rev. 5 board has vias behind expansion-connector pins 1, 3 and 5, and a Rev. 3 board only behind pins 1 and 3. Rev. 8A boards, silkscreened "A500+", were made for the Amiga 500 Plus and are not covered by these lists; they fit the A500 case, so the badge on the case does not identify the board.

Rev. 6A/7 main board

PCB assembly 312510 Rev. 6A/7, aluminium electrolytics

Ref	Capacitance	Rating	Type	Commodore part
C306, C712	10 µF	16 V	Radial	390101-06
C303, C304, C324, C334	22 µF	35 V	Radial	390101-04
C821, C822	47 µF	35 V	Radial	390101-01
C811, C812, C813, C814, C815, C816	100 µF	16 V	Radial	390101-02
C307	470 µF	16 V	Radial	390101-03
C401, C402	3300 µF	10 V	Radial	900100-56

That is 17 electrolytics. Commodore's audio troubleshooting names C324 in the left audio output path and C334 in the right, each with an EMI filter between it and the output jack.

Rev. 5 main board

PCB assembly 312510 Rev. 5, electrolytics as printed

Ref	Capacitance	Rating printed	Commodore part
C306, C712	10 µF	Not printed	390101-06
C303, C304, C307, C334	22 µF	Not printed	390101-04
C812, C813, C814, C815, C821, C822	47 µF	Not printed	390101-01
C307, C811	100 µF	Not printed	390101-02
C401, C402	3300 µF	10 V	900100-56

Two things in this list need care. C307 is printed in both the 22 µF and the 100 µF rows, and C324, which the audio troubleshooting section names in the left channel, is missing from it. Commodore's Rev. 5 schematic settles both: it shows C307 as 100 µF across Paula's +5 V supply and C324 as 22 µF in the left audio output, beside C334 in the right, which suggests that the C307 printed in the 22 µF row is a misprint for C324. Retro Rewind's Rev. 3/5 kit list gives the same two values. The Rev. 5 list gives no voltage ratings except for C401 and C402, but it uses the same Commodore part numbers as the Rev. 6A/7 list, which does: 390101-06 is 10 µF 16 V, 390101-04 is 22 µF 35 V, 390101-01 is 47 µF 35 V and 390101-02 is 100 µF 16 V.

A501 RAM and clock expansion

The A501 board layout, assembly 312604, with the clock and battery along the lower edge

A501 assembly 312604-04 Rev. 6C

Ref	Capacitance	Rating	Type
C902, C903	100 µF	16 V	Aluminium, radial (390101-02)
C913	4.7 µF	16 V	Tantalum (900410-13) or aluminium (390101-05)

The A501's NiCd battery, BT9 in the parts list, causes far more damage than its capacitors; replace it at the same time. See the maintenance guide.

Other lists

Kit sellers' lists are secondary sources and differ from Commodore's. Console5's list for 312510-07, a community list read from boards, is marked "unconfirmed": it adds C615 (100 µF) and C722 (47 µF), which appear in neither Commodore list, includes C902 and C903, which are A501 positions, and gives C821 and C822 as 16 V where Commodore lists 35 V. Retro Rewind's kit list covers Rev. 3 and Rev. 5 boards with one list and Rev. 6/6A with another. It gives some positions higher ratings than Commodore, for example C307 at 25 V on Rev. 6A, and states that its kits use "equal or higher rated capacitors". A higher voltage rating at the same capacitance is acceptable if the part fits.

The internal Chinon FB-354 floppy drive has its own electrolytics; one restorer lists three 22 µF and one 1 µF.

Procedure

1. Disconnect the power supply and remove the top case, keyboard and RF shield.
2. Note the board's assembly number and use the matching table. Photograph the board before removing anything.
3. Mark the polarity of each electrolytic on the board or in your photographs. The negative stripe on the sleeve marks the negative lead.
4. Remove one capacitor at a time. Heat each joint and clear it with a desoldering tool; do not pull a lead through a plated hole.
5. Fit a new part of the same capacitance and at least the listed voltage, checking polarity before soldering. Use radial parts with the original lead spacing.
6. Check the solder side for bridges, clean off flux, and power up with the case open.

Checks after the recap

Commodore's preliminary checks, taken to a ±10 % tolerance:

Supply checks, A500 service manual section 3

Point	Expected
CN12 (floppy power) pin 1	+5 V
CN12 pin 4	+12 V
U38 (MC1488) pin 1	−12 V

Then confirm sound from both audio outputs, since C324 and C334 sit in the output paths.

Related pages

• Amiga 500
• Amiga 500 Maintenance Guide
• Amiga 500 Troubleshooting Guide
• Amiga 500 Service Manual (314981-04)
• Capacitor Failure Symptoms
• Recommended Tools